Existing radio systems (GSM, Global System for Mobile Communications; WCDMA/HSDPA, Wide-band Code Division Multiple Access/High Speed Downlink Packet Access) are not optimally suited for, for example, downloading movies from the Internet since they have been developed and defined under the assumption of a coordinated network deployment.
To alleviate the problem, a user can acquire a private base station for his/her own disposal. The private base stations are typically associated with uncoordinated and large-scale deployment. A private base station may be called with many names, such as Home Base Station, Home NodeB, femto eNodeBs or simply Home Access, and it has become a popular topic within the operator and manufacturer community.
It can be assumed that the end-user buys an economic private base station and installs the physical entity at his home. The private base station then provides coverage and service to the user equipment registered by the owner of the private base station. Still, the private base station may use the same spectrum as the radio system. The private base station may be connected via a DSL (Digital Subscriber Line) and via the core network of the operator towards the Internet. Some local breakout scenarios bypassing the core network of the operator may also exist. In any case the consumed services of the owner of a private base station do not eat up capacity of the radio system.
A major requirement for private base stations is that the system supports efficient mechanisms to restrict access to a private base station unless user equipment have access rights to communicate with a specific private base station. Correspondingly, user equipment should not unnecessarily attempt to camp on a cell of a private base station if they do not have access rights.
User equipment is able to extend its list of the private base station it has access to. In UMTS (Universal Mobile Telecommunications System), access to regionally restricted areas are handled via a list of “forbidden Location Areas for roaming” and a list of “forbidden location areas for regional provision of service”. These lists in the user equipment are erased when the user equipment is switched off or when the SIM/USIM (Subscriber Identity Module/Universal SIM) is removed, and even regularly in a period of 12/24 hours, for instance. A new entry—corresponding to the LAI (Location Area Identification) received on the broadcast channel—can be added to one of those lists. For LTE/SAE (Long Term Evolution/System Architecture Evolution), a similar list can be defined for Tracking Areas and can be stored in the user equipment. A similar list does exist for PLMNs (Public Land Mobile Network) as well.
In general, concepts relying on NAS (Non-Access-Stratum) procedures can generate a lot of signaling between private base stations, user equipment and the core network, as user equipment need to learn about their restrictions once they attempt to contact a private base station. Given the limitation of user equipment to store lots of forbidden LAIs, it might well happen that user equipment on a daily trip through a city erases its forbidden LAI list several times and hence generates the necessity to contact the network in vain on daily (or shorter) basis, introducing unnecessary power consumption and battery drain, etc.
Initiated NAS procedures generate signaling, which increases interference and should thus be avoided. The NAS procedures may also cause security problems, if for instance intermediate gateways, which serve the private base stations and which do not have security keys of the user equipment available, request the user equipment to authenticate itself with permanent user equipment identifications like IMSI (International Mobile Subscriber Identity) or IMEI (International Mobile Equipment Identity).